Upset odds badly (5)
I believe the answer is:
spill
'upset' is the definition.
(thesaurus)
'odds badly' is the wordplay.
'odds' becomes 'sp' (betting abbreviation for starting price).
'badly' becomes 'ill' ('ill' can be adverbial as in 'ill-advised').
'sp'+'ill'='SPILL'
(Other definitions for spill that I've seen before include "Upset - lighter" , "Accidentally cause to overflow" , "Tip" , "Allow to drop - fire lighter" , "Shed" .)